This invention relates to a control signal generator of the type which is capable of generating two different types of control signals as a function of the setting of an adjustable resistance and, more particularly, to such a control signal generator wherein a first control signal has an amplitude which is a function of the setting of the resistance, and the second control signal has its level changed over from a first to a second level at a predetermined setting of the resistance.
Various applications are known for a control signal generator of the type described above. For example, in one use thereof, the control signal generator functions to control the operation of an induction heating device. Typically, an induction heating device includes an induction element, such as an induction coil, which is supplied with a rectified, filtered AC signal, and which is connected in series with a high frequency switch which operates to periodically interrupt the rectified current flowing through the coil. Such current interruptions result in an alternating flux of high frequency. If a conductive material is placed in this alternating flux, eddy currents are induced therein, and these currents generate heat. The frequency of the flux alternations is, of course, controlled by the switching frequency, and the amount of heat generated by the induction heating device is inversely related to this switching frequency. Thus, the amount of generated heat can be regulated by controlling the switching frequency of the switch.
Furthermore, in such an induction heating device, the rectified current which is supplied to the induction coil should be generated by a convertible rectifier, that is, a rectifier which is capable of operating either as a half-wave or as a full-wave rectifier. Of course, the magnitude of the rectified current which is produced by half-wave rectification is less than the magnitude of the current which is produced by full-wave rectification. Accordingly, the magnitude of the flux which is produced by the induction coil can be selected to be relatively low by operating the rectifier as a half-wave rectifier, thus generating a relatively low range of heat; or the flux can be selected to be relatively high by operating the rectifier as a full-wave rectifier, thus generating a relatively high range of heat.
In an induction heating device of the aforedescribed type, it is convenient to provide a single adjustable element, such as a potentiometer, for determining both the switching frequency of the switch and the half/full wave rectification mode of the rectifier. Thus, if the setting of the potentiometer increases from a minimum setting towards its maximum setting, a continuously varying control signal should be produced which is a function of the potentiometer setting. This control signal is used to control the switching frequency. Furthermore, when the potentiometer setting is within a relatively low range, another control signal should be produced for selecting the half-wave rectification mode of the rectifier. Then, when a predetermined setting of the potentiometer is reached, the frequency control signal should return abruptly to its initial level while, concurrently, the rectification control signal should change over so as to establish a full-wave rectification mode. Then, further increases in the setting of the potentiometer should result in a corresponding increase in the frequency control signal, whereby the heat generated by the induction coil now is increased over a second, higher range.
A control signal generator which generates a first, continuously variable, repeatable control signal as well as a step-wise control signal also is useful in controlling the operation of either one of two different devices in response to the setting of a single adjustable element. When the setting of the adjustable element is within a first range, the level of the step-wise control signal is such that one of the devices is selected to be controlled as a function of the continuously varying control signal. Then, when the setting of the adjustable element reaches the second range, the level of the step-wise control signal changes so that the second device is selected to be controlled. At the same time, the continuously varying control signal returns to an initial amplitude thereof to obtain proper control over this second device.
Yet another application of a control signal generator of the aforedescribed type is to control a single device over two separate ranges as a function of the setting of a single adjustable element. In such an environment, when the step-wise control signal is at one level, the gain of the overall control system which is used with the control signal generator is set at, for example, a lower level, whereby the operation of the device is controlled as a function of the continuously varying control signal. Then, when the level of the step-wise control signal changes, the overall gain of the control system also changes, for example, to a higher level, and the device now is controlled over a higher operating range as a function of the continuously varying control signal.